Activation Spectra of 700 mμ Absorption Change in Photosynthesis

In previous papers (1-3) we reported the occurrence of a light induced fast reversible absorption decrease around 700 m,u in photosynthetic organisms. The effect was ascribed to the photochemical bleaching of a pigment (P700) present in low concentration followed by a spontaneous regeneration in the dark. Such a mechanism predicts that the average concentration level of P700 is determined by the balance between photochemical destruction and dark restoration. However, we later observed with the blue green alga Anacystis (4) that light of certain spectral composition (red) raises rather than lowers this steady state level, and in this respect functions antagonistic to light of other wavelengths (far red). The following paper describes experiments in which we have attempted to determine activation spectra of the fast photochemical bleaching, as well as of the light induced increase of steady state absorption. Other observations concern the intensity relations between the two light effects, and the fraction of absorbed light possibly funneled through P700 turnover.